Table 38. Stabilized restricted earth-fault protection (LREFPNDF)
Characteristic
Value
Operation accuracy
At the frequency f = f
n
±1.5% of the set value or ±0.002 × I
n
Start time
1)2)
I
Fault
= 2.0 × set
Operate value
I
Fault
=
10.0 × set
Operate
value
Typical 18 ms (±5 ms)
Typical 12 ms (±5 ms)
Reset time
< 50 ms
Reset ratio
Typical 0.96
Retardation time
< 35 ms
Operate time accuracy in definite time mode
±1.0% of the set value or ±20 ms
Suppression of harmonics
DFT: -50 dB at f = n × f
n
, where n = 2, 3, 4,
5, …
1) Current before fault = 0.0 × I
n
, f
n
= 50 Hz
2) Includes the delay of the signal output contact
Table 39. Stabilized restricted earth-fault protection (LREFPNDF) main settings
Parameter
Function
Value (Range)
Step
Operate value
LREFPNDF
5...50 %
1
Restraint mode
LREFPNDF
None
2nd harmonic
-
Start value 2.H
LREFPNDF
10...50 %
1
Minimum operate
time
LREFPNDF
0.040...300.000 s
0.001
Transformer Protection and Control
1MRS756978 D
RET630
Product version: 1.1
Issued: 2011-05-18
ABB
37